I used to have a friend do machine work for me (Custom Engines here in Melbourne AU). He was far from cheap, but did alot of high end stuff, including the first 6 second Pro Stock car in Australia. We had a falling out (more so him than me anyway), so I will be looking around for a new machine shop. My old machinist's brother and I have talked about setting up a shop, but that is a long ways off at the moment.
The engine assembly I usually do myself, I am a CNC Machinist and I am fussy. I am happy spending the extra time getting stuff 100% to my satisfaction, whereas a shop would go broke doing the same thing. In saying that, I was lazy and got my fore mentioned friend (Con Sagiaris) to put my current engine together. He is one of the few engine builders I trust, most of them down here are hacks, there is far too much near enough is good enough. But I could probably say the same for engine builders in other parts of the world.